| Issue |
143379
|
| Summary |
[X86_64] Incorrect value of local variable after longjmp with optimizatio
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
hutuhutong
|
Summary
When compiling the following C code with optimization level -O1, the local variable x exhibits unexpected behavior. In principle, under optimization levels -O1, -O2, and -O3, Clang should treat the allocation and modification of the variable x in a consistent manner. However, when the statement printf("Address of x: %p\n", (void*)&x); is included, a different result is observed at -O1, indicating inconsistent optimization behavior. This suggests that Clang handles the optimization of the printf call involving the address of x in a non-uniform way.
Details
========test.c========
#include <stdio.h>
#include <setjmp.h>
#include <stdlib.h>
void test_gamma() {
int x=0;
jmp_buf env;
if (setjmp(env)) {
printf("Jumped here\n");
} else {
x = 42;
longjmp(env, 1);
}
printf("Value of x: %d Address of x: %p\n", x, (void*)&x);
}
void test_gamma1() {
int x=0;
jmp_buf env;
if (setjmp(env)) {
printf("Jumped here\n");
} else {
x = 42;
longjmp(env, 1);
}
int a = x*1;
printf("Value of x: %d %d\n", x, a);
}
int main() {
test_gamma();
test_gamma1();
return 0;
}
========output========
$ clang -O0 test.c -o test
$ ./test
Jumped here
Value of x: 42 Address of x: 0x7ffc7979655c
Jumped here
Value of x: 42 42
$ clang -O1 test.c -o test
$ ./test
Jumped here
Value of x: 42 Address of x: 0x7ffd6dc09afc
Jumped here
Value of x: 0 0
$ clang -O2 test.c -o test
$ ./test
Jumped here
Value of x: 0 Address of x: 0x7ffceb8ec25c
Jumped here
Value of x: 0 0
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